tree-optimization/93946 - fix bogus redundant store removal in FRE, DSE and DOM

This fixes a common mistake in removing a store that looks redudnant but
is not because it changes the dynamic type of the memory and thus makes
a difference for following loads with TBAA.

2020-03-03  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/93946
	* alias.h (refs_same_for_tbaa_p): Declare.
	* alias.c (refs_same_for_tbaa_p): New function.
	* tree-ssa-alias.c (ao_ref_alias_set): For a NULL ref return
	zero.
	* tree-ssa-scopedtables.h
	(avail_exprs_stack::lookup_avail_expr): Add output argument
	giving access to the hashtable entry.
	* tree-ssa-scopedtables.c (avail_exprs_stack::lookup_avail_expr):
	Likewise.
	* tree-ssa-dom.c: Include alias.h.
	(dom_opt_dom_walker::optimize_stmt): Validate TBAA state before
	removing redundant store.
	* tree-ssa-sccvn.h (vn_reference_s::base_set): New member.
	(ao_ref_init_from_vn_reference): Adjust prototype.
	(vn_reference_lookup_pieces): Likewise.
	(vn_reference_insert_pieces): Likewise.
	* tree-ssa-sccvn.c: Track base alias set in addition to alias
	set everywhere.
	(eliminate_dom_walker::eliminate_stmt): Also check base alias
	set when removing redundant stores.
	(visit_reference_op_store): Likewise.
	* dse.c (record_store): Adjust valdity check for redundant
	store removal.

	* gcc.dg/torture/pr93946-1.c: New testcase.
	* gcc.dg/torture/pr93946-2.c: Likewise.

1 files changed, 20 insertions, 0 deletions

diff --git a/gcc/alias.c b/gcc/alias.c
index fe75e22cdb5..d38e386d0e8 100644
--- a/gcc/alias.c
+++ b/gcc/alias.c
@@ -368,6 +368,26 @@ rtx_refs_may_alias_p (const_rtx x, const_rtx mem, bool tbaa_p)
 			     && MEM_ALIAS_SET (mem) != 0);
 }
 
+/* Return true if the ref EARLIER behaves the same as LATER with respect
+   to TBAA for every memory reference that might follow LATER.  */
+
+bool
+refs_same_for_tbaa_p (tree earlier, tree later)
+{
+  ao_ref earlier_ref, later_ref;
+  ao_ref_init (&earlier_ref, earlier);
+  ao_ref_init (&later_ref, later);
+  alias_set_type earlier_set = ao_ref_alias_set (&earlier_ref);
+  alias_set_type later_set = ao_ref_alias_set (&later_ref);
+  if (!(earlier_set == later_set
+	|| alias_set_subset_of (later_set, earlier_set)))
+    return false;
+  alias_set_type later_base_set = ao_ref_base_alias_set (&later_ref);
+  alias_set_type earlier_base_set = ao_ref_base_alias_set (&earlier_ref);
+  return (earlier_base_set == later_base_set
+	  || alias_set_subset_of (later_base_set, earlier_base_set));
+}
+
 /* Returns a pointer to the alias set entry for ALIAS_SET, if there is
    such an entry, or NULL otherwise.  */